/* Design tokens */
:root {
  --bg: #fbf7ef;
  --surface: #fffdf8;
  --text: #231f1a;
  --muted: #766f66;
  --border: #e8ded0;
  --primary: #2d2924;
  --accent: #c2410c;
  --success: #15803d;
  --warning: #b45309;
  --radius: 8px;
  --sidebar-w: 280px;
}

/* Reset */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Noto Sans SC", "PingFang SC", "Microsoft YaHei", sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}

/* Layout */
#app { display: flex; min-height: 100vh; }

/* Sidebar */
#sidebar {
  width: var(--sidebar-w);
  background: var(--primary);
  color: #e8ded0;
  display: flex;
  flex-direction: column;
  position: fixed;
  top: 0; left: 0; bottom: 0;
  z-index: 10;
  overflow-y: auto;
}

#sidebar-header {
  padding: 24px 20px 16px;
  border-bottom: 1px solid rgba(232,222,208,0.15);
}

#course-badge {
  font-size: 11px;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: #f08a4b;
  margin-bottom: 6px;
}

#sidebar-title {
  font-size: 17px;
  font-weight: 600;
  color: #fffdf8;
  line-height: 1.35;
  margin-bottom: 10px;
}

#progress-summary { font-size: 13px; color: #9c9488; }
#progress-count { color: #f08a4b; font-weight: 600; }

/* Nav items */
#lesson-nav {
  list-style: none;
  flex: 1;
  padding: 12px 0;
}

.nav-item {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 9px 20px;
  cursor: pointer;
  transition: background 0.15s;
  font-size: 14px;
}

.nav-item:hover { background: rgba(255,255,255,0.06); }
.nav-item.active { background: rgba(194,65,12,0.18); border-right: 3px solid var(--accent); }

.nav-number {
  width: 28px; height: 28px;
  border-radius: 50%;
  background: rgba(255,255,255,0.08);
  display: flex; align-items: center; justify-content: center;
  font-size: 13px; font-weight: 600;
  flex-shrink: 0;
}

.nav-number.nav-special { background: var(--accent); color: #fff; }

.nav-item.completed .nav-number { background: var(--success); color: #fff; }
.nav-item.completed .nav-label { color: #9c9488; }

.nav-label { color: #d4cdc2; }

/* Sidebar footer */
#sidebar-footer {
  padding: 14px 20px;
  border-top: 1px solid rgba(232,222,208,0.15);
}

#back-to-course {
  display: block;
  color: #fff;
  font-size: 13px;
  text-decoration: none;
  padding: 12px 20px 8px;
}

#back-to-course:hover { opacity: 0.8; }

#reset-progress {
  color: #9c9488;
  font-size: 12px;
  text-decoration: none;
}

#reset-progress:hover { color: var(--accent); }

/* Main */
#main {
  flex: 1;
  margin-left: var(--sidebar-w);
  min-height: 100vh;
}

.view { display: none; padding: 48px 56px; max-width: 780px; }
.view.active { display: block; }

/* Overview */
#hero {
  margin-bottom: 48px;
}

#hero h1 {
  font-size: 36px;
  font-weight: 700;
  line-height: 1.25;
  margin-bottom: 12px;
  letter-spacing: -0.02em;
}

#hero-desc {
  font-size: 16px;
  color: var(--muted);
  max-width: 600px;
  margin-bottom: 12px;
  line-height: 1.6;
}

#hero-meta {
  font-size: 13px;
  color: var(--muted);
  margin-bottom: 24px;
}

#start-btn {
  display: inline-block;
  background: var(--accent);
  color: #fff;
  border: none;
  padding: 12px 32px;
  font-size: 15px;
  font-weight: 600;
  border-radius: var(--radius);
  cursor: pointer;
  transition: background 0.15s;
}

#start-btn:hover { background: #a3360a; }

/* Lesson cards on overview */
#lesson-cards {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: 16px;
}

.lesson-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px 22px;
  cursor: pointer;
  transition: box-shadow 0.15s, border-color 0.15s;
}

.lesson-card:hover {
  border-color: var(--accent);
  box-shadow: 0 2px 12px rgba(0,0,0,0.06);
}

.lesson-card-number {
  font-size: 12px;
  font-weight: 700;
  color: var(--accent);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 4px;
}

.lesson-card-title {
  font-size: 16px;
  font-weight: 600;
  margin-bottom: 6px;
}

.lesson-card-concepts {
  font-size: 13px;
  color: var(--muted);
  line-height: 1.5;
}

/* Lesson view */
#lesson-header {
  margin-bottom: 12px;
}

#lesson-number {
  font-size: 12px;
  font-weight: 700;
  color: var(--accent);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 2px;
}

#lesson-title {
  font-size: 28px;
  font-weight: 700;
  line-height: 1.3;
  letter-spacing: -0.01em;
}

#lesson-goal {
  background: var(--surface);
  border: 1px solid var(--border);
  border-left: 3px solid var(--accent);
  border-radius: var(--radius);
  padding: 14px 18px;
  margin-bottom: 24px;
  font-size: 16px;
  color: var(--muted);
}

#lesson-goal strong { color: var(--text); }

/* Objectives */
#objectives-block {
  margin-bottom: 28px;
}

#objectives-block h3 {
  font-size: 18px;
  font-weight: 600;
  margin-bottom: 8px;
}

#objectives-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 6px;
}

#objectives-list li {
  padding-left: 20px;
  position: relative;
  font-size: 16px;
}

#objectives-list li::before {
  content: "→";
  position: absolute;
  left: 0;
  color: var(--accent);
  font-weight: 600;
}

/* Lesson body */
#lesson-body {
  margin-bottom: 32px;
}

#lesson-body p {
  margin-bottom: 14px;
  font-size: 16px;
}

#lesson-body .example-box {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 16px 18px;
  margin-bottom: 16px;
}

#lesson-body .example-box .example-label {
  font-size: 11px;
  font-weight: 700;
  color: var(--accent);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 8px;
}

#lesson-body .example-box .chat-msg {
  margin-bottom: 8px;
  font-size: 16px;
}

#lesson-body .example-box .chat-msg:last-child { margin-bottom: 0; }

#lesson-body .example-box .chat-msg .role {
  font-weight: 600;
  font-size: 12px;
  margin-bottom: 2px;
}

#lesson-body .example-box .chat-msg .role.user { color: #2563eb; }
#lesson-body .example-box .chat-msg .role.ai { color: var(--accent); }

#lesson-body .example-box .chat-msg .msg-text {
  color: var(--text);
  padding-left: 8px;
  border-left: 2px solid var(--border);
}

#lesson-body .insight {
  background: rgba(194,65,12,0.06);
  border: 1px solid rgba(194,65,12,0.15);
  border-radius: var(--radius);
  padding: 14px 18px;
  margin-bottom: 16px;
  font-size: 16px;
}

#lesson-body .insight strong { color: var(--accent); }

/* Flashcards */
#flashcards-block {
  margin-bottom: 32px;
}

#flashcards-block h3 {
  font-size: 18px;
  font-weight: 600;
  margin-bottom: 4px;
}

.block-hint {
  font-size: 12px;
  color: var(--muted);
  margin-bottom: 12px;
}

#flashcards-container {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 12px;
}

.flashcard {
  height: 140px;
  perspective: 600px;
  cursor: pointer;
}

.flashcard-inner {
  width: 100%; height: 100%;
  position: relative;
  transition: transform 0.4s;
  transform-style: preserve-3d;
}

.flashcard.flipped .flashcard-inner { transform: rotateY(180deg); }

.flashcard-front, .flashcard-back {
  position: absolute;
  width: 100%; height: 100%;
  backface-visibility: hidden;
  border-radius: var(--radius);
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  padding: 20px;
  font-size: 16px;
  line-height: 1.5;
}

.flashcard-front {
  background: var(--surface);
  border: 1px solid var(--border);
  font-weight: 500;
}

.flashcard-back {
  background: var(--primary);
  color: #fffdf8;
  transform: rotateY(180deg);
}

.flashcard-back code {
  background: rgba(255,255,255,0.12);
  padding: 2px 6px;
  border-radius: 3px;
  font-size: 13px;
}

/* Quiz */
#quiz-block { margin-bottom: 32px; }

#quiz-block h3 {
  font-size: 18px;
  font-weight: 600;
  margin-bottom: 12px;
}

.quiz-question {
  margin-bottom: 20px;
}

.quiz-question .q-text {
  font-weight: 600;
  margin-bottom: 10px;
  font-size: 16px;
}

.quiz-option {
  display: block;
  width: 100%;
  text-align: left;
  padding: 10px 14px;
  margin-bottom: 6px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  font-size: 16px;
  cursor: pointer;
  transition: border-color 0.15s, background 0.15s;
}

.quiz-option:hover:not(.disabled) { border-color: var(--accent); }
.quiz-option.disabled { cursor: default; }

.quiz-option.correct {
  border-color: var(--success);
  background: rgba(21,128,61,0.08);
}

.quiz-option.incorrect {
  border-color: var(--accent);
  background: rgba(194,65,12,0.08);
}

.quiz-option.show-correct {
  border-color: var(--success);
  background: rgba(21,128,61,0.06);
}

.quiz-feedback {
  font-size: 16px;
  padding: 8px 14px;
  margin-top: 6px;
  border-radius: var(--radius);
  display: none;
}

.quiz-feedback.show { display: block; }

.quiz-feedback.correct-fb {
  background: rgba(21,128,61,0.08);
  color: var(--success);
}

.quiz-feedback.incorrect-fb {
  background: rgba(194,65,12,0.08);
  color: var(--accent);
}

/* Sources */
#sources-block { margin-bottom: 32px; }

#sources-block h3 {
  font-size: 18px;
  font-weight: 500;
  color: var(--muted);
  margin-bottom: 6px;
}

.source-card {
  display: block;
  font-size: 12px;
  color: var(--muted);
  text-decoration: none;
  margin-bottom: 3px;
}

.source-card:hover { color: var(--accent); }

.source-card .source-label { font-weight: 500; }

.source-card .source-url {
  opacity: 0.7;
  margin-left: 4px;
}

/* Lesson nav buttons */
#lesson-nav-buttons {
  display: flex;
  justify-content: space-between;
  margin-top: 40px;
  padding-top: 20px;
  border-top: 1px solid var(--border);
}

.nav-btn {
  padding: 9px 20px;
  font-size: 14px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  cursor: pointer;
  color: var(--text);
  transition: border-color 0.15s, background 0.15s;
}

.nav-btn:hover { border-color: var(--accent); background: #fff; }
.nav-btn:disabled { opacity: 0.35; cursor: default; }

/* Final review */
.final-score {
  text-align: center;
  padding: 32px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  margin-bottom: 24px;
}

.final-score .score-number {
  font-size: 48px;
  font-weight: 700;
  color: var(--accent);
}

.final-score .score-label {
  font-size: 14px;
  color: var(--muted);
  margin-top: 4px;
}

/* ── Hamburger toggle ─────────────────────────────────────── */
.sidebar-toggle { display: none; }
.sidebar-toggle-label { display: none; }
.sidebar-overlay { display: none; }

/* ── Responsive ───────────────────────────────────────────── */
@media (max-width: 768px) {
  .sidebar-toggle-label {
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    gap: 5px;
    position: fixed;
    top: 14px;
    right: 14px;
    z-index: 110;
    width: 40px;
    height: 40px;
    cursor: pointer;
    background: var(--primary);
    border-radius: var(--radius);
  }

  .sidebar-toggle-label span {
    display: block;
    width: 20px;
    height: 2px;
    background: #e8ded0;
    border-radius: 2px;
    transition: transform 0.25s, opacity 0.25s;
  }

  .sidebar-toggle:checked ~ .sidebar-toggle-label span:nth-child(1) {
    transform: translateY(7px) rotate(45deg);
  }
  .sidebar-toggle:checked ~ .sidebar-toggle-label span:nth-child(2) {
    opacity: 0;
  }
  .sidebar-toggle:checked ~ .sidebar-toggle-label span:nth-child(3) {
    transform: translateY(-7px) rotate(-45deg);
  }

  .sidebar-overlay {
    display: none;
    position: fixed;
    inset: 0;
    background: rgba(0,0,0,0.4);
    z-index: 20;
  }
  .sidebar-toggle:checked ~ .sidebar-overlay { display: block; }

  #sidebar {
    position: fixed;
    top: 0; left: 0; bottom: 0;
    width: 280px;
    z-index: 30;
    transform: translateX(-100%);
    transition: transform 0.3s ease;
    overflow-y: auto;
  }
  .sidebar-toggle:checked ~ #sidebar { transform: translateX(0); }

  #sidebar-header { padding: 18px 16px 12px; }
  #sidebar-title { font-size: 15px; }
  #course-badge { font-size: 10px; }
  #progress-summary { font-size: 12px; }

  #lesson-nav { padding: 8px 0; }

  .nav-item {
    padding: 10px 16px;
    font-size: 14px;
    min-height: 44px;
  }

  .nav-number { width: 28px; height: 28px; font-size: 12px; }
  #sidebar-footer { padding: 12px 16px; }

  #main { margin-left: 0; }

  .view { padding: 20px 16px 32px; max-width: 100%; }

  #hero { margin-bottom: 32px; }
  #hero h1 { font-size: 22px; line-height: 1.3; }
  #hero-desc { font-size: 14px; margin-bottom: 8px; }
  #hero-meta { font-size: 12px; margin-bottom: 18px; }
  #start-btn { padding: 12px 28px; font-size: 15px; width: 100%; text-align: center; }

  #lesson-cards { grid-template-columns: 1fr; gap: 10px; }
  .lesson-card { padding: 16px 18px; min-height: 44px; }
  .lesson-card-title { font-size: 15px; }
  .lesson-card-concepts { font-size: 12px; }

  #lesson-title { font-size: 20px; }
  #lesson-number { font-size: 11px; }
  #lesson-goal { padding: 12px 14px; font-size: 13px; }

  #objectives-block { margin-bottom: 22px; }
  #objectives-block h3 { font-size: 14px; }
  #objectives-list li { font-size: 13px; padding-left: 18px; }

  #lesson-body { margin-bottom: 24px; }
  #lesson-body p { font-size: 14px; margin-bottom: 10px; }
  #lesson-body .example-box { padding: 12px 14px; }
  #lesson-body .example-box .example-label { font-size: 10px; }
  #lesson-body .example-box .chat-msg { font-size: 13px; }
  #lesson-body .example-box .chat-msg .msg-text { padding-left: 6px; }
  #lesson-body .insight { padding: 12px 14px; font-size: 13px; }

  #flashcards-block { margin-bottom: 24px; }
  #flashcards-block h3 { font-size: 14px; }
  #flashcards-container { grid-template-columns: 1fr; gap: 10px; }
  .flashcard { height: 120px; }
  .flashcard-front, .flashcard-back { font-size: 13px; padding: 14px; }

  #quiz-block { margin-bottom: 24px; }
  #quiz-block h3 { font-size: 14px; }
  .quiz-question { margin-bottom: 16px; }
  .quiz-question .q-text { font-size: 14px; }
  .quiz-option { font-size: 13px; padding: 12px 14px; min-height: 44px; }
  .quiz-feedback { font-size: 12px; }

  #sources-block { margin-bottom: 24px; }
  #sources-block h3 { font-size: 12px; }
  .source-card { font-size: 11px; }
  .source-card .source-url { word-break: break-all; }

  #lesson-nav-buttons {
    margin-top: 28px; padding-top: 14px;
    position: sticky; bottom: 0;
    background: var(--bg); padding-bottom: 8px;
  }

  .nav-btn { padding: 10px 18px; font-size: 13px; min-height: 44px; min-width: 44px; }

  .final-score { padding: 24px 16px; }
  .final-score .score-number { font-size: 36px; }
  .final-score .score-label { font-size: 13px; }
}

@media (max-width: 400px) {
  #hero h1 { font-size: 20px; }
  #lesson-title { font-size: 18px; }
  .view { padding: 14px 12px 24px; }
  .flashcard { height: 110px; }
  .flashcard-front, .flashcard-back { font-size: 12px; padding: 10px; }
}